1. Field of the Invention
The present invention relates to a technique of recording dots on the surface of a printing medium, so as to print an image.
2. Description of the Related Art
Typical examples of the dot recording apparatus that records dots while scanning a dot record head in a main scanning direction and in a sub-scanning direction include serial scan printers and drum scan printers. Parameters defining the dot recording mode in such printers include the number of nozzles used for printing with regard to one color, the nozzle pitch, and the feeding amounts of sub-scan. One printer may adopts a plurality of different dot recording modes having different settings for some of these parameters.
Pixels, which are the measure for defining the dot recording position, are virtually arranged along the width and the length of a printing medium. An array of pixels arranged in the main scanning direction on the printing medium is called a raster line. For the high-quality printing result, it is desirable to record dots on the respective raster lines at equal intervals in the sub-scanning direction. The manufacturing error of an individual dot recording apparatus may, however, cause the dots on the respective raster lines to be not recorded at equal intervals in the sub-scanning direction. One proposed technique disclosed in JP10-337864A selects the dot recording mode suitable for each dot recording apparatus, which has a little variation in dot array interval in the sub-scanning direction, among a plurality of dot recording modes by taking into account the manufacturing error of the dot recording apparatus.
This prior art technique measures the distance between raster lines actually recorded in each dot recording mode and selects a desired dot recording mode based on the measurement results. This method records linear ruled lines on the raster lines with regard to all the possible combinations of nozzles that may record adjoining raster lines. The method of actually printing the ruled lines with regard to all the combinations of the nozzles and the sub-scan feeds in the respective dot recording modes is a heavy load and takes a significantly long time.
The object of the present invention is thus to provide a technique that enables a desired dot record mode to be readily set in an individual dot recording apparatus.
In order to attain at least part of the above and other objects, the present invention applies some technique to recording dots on a printing medium with a dot record head having a plurality of dot forming elements, which are used to form dots on the printing medium, by carrying out main scan and sub-scan, where the main scan shifts at least one of the dot record head and the printing medium in a main scanning direction and the sub-scan shifts at least one of the dot record head and the printing medium in a sub-scanning direction perpendicular to the main scanning direction. First displacement data is generated which substantially represents deviations of dot recording positions in the sub-scanning direction with respect to the plurality of dot forming elements from a reference dot recording position by a reference dot forming element selected among the plurality of dot forming elements. Second displacement data is also generated which substantially represents feeding errors of the sub-scan in the sub-scanning direction. Then a dot record mode is selected among a plurality of dot record modes, based on the first displacement data and the second displacement data, each of the dot record modes specifying operations of the main scan and the sub-scan to record dots, the plurality of dot record modes having a same dot resolution and a substantially same recording speed but different combinations of feeding amounts for the sub-scan carried out in respective intervals of adjoining passes of the main scan. Then the main scan and the sub-scan are carried out to record dots in the selected dot record mode.
This arrangement enables a deviation of dot recording position on each raster line to be checked easily without actually recording dots on the raster line. The optimum dot record mode is then selected, based on the information regarding the displacement of dot recording position.
When the dot record head is replaceable, it is preferable that the first displacement data is stored in the first storage unit provided on the dot record head. Even when the dot record head is replaced with a new one, this arrangement enables a desired dot record mode suitable for the new dot record head to be selected.
One applicable dot recording method carries out the sub-scan by a predetermined combination of feeding amounts in respective intervals of adjoining sub-scan feeds, so as to record dots on each raster line on the printing medium. In this dot recording method, it is preferable that the dot record mode is selected according to the procedure discussed below. A sum of accumulated feeding errors of the sub-scan and a deviation of a dot recording position in the sub-scanning direction is calculated. The accumulated feeding errors of the sub-scan is the errors with respect to each raster line of interest efore the raster line of interest on the printing medium is recorded. The deviation of a dot recording position in the sub-scanning direction is the deviation by a dot forming element used for recording the raster line of interest from the reference dot recording position. The sum is specified as a displacement of dot recording position on each raster line. A evaluation value relating to a variation in intervals of adjoining raster lines in the sub-scanning direction is calculated based on the displacement of dot recording position on each raster line on the printing medium, and selecting the dot record mode according to the evaluation value.
This arrangement enables the displacement of dot recording position to be calculated with high accuracy from the feeding errors of sub-scan and the deviation of the dot recording position with regard to the corresponding dot forming element.
It is preferable that the displacement of dot recording position is calculated with regard to an equal number of raster lines in each of the dot record modes. This application ensures the accurate evaluation of the displacement and the selection of the appropriate dot record mode even when the evaluation value is affected by the number of samples.
The displacement of dot recording position may be calculated with regard to raster lines to be recorded while one set of the sub-scan is carried out by the combination of feeding amounts for each dot record mode. When the respective feeding amounts of sub-scan included in the combination set for each dot record mode have intrinsic errors, the arrangement of calculating the displacement of dot recording position on each of the above raster lines ensures the appropriate evaluation of the displacement in each dot record mode.
The second displacement data may be generated according to the following procedure. The dot record head is shifted in a direction identical with the main scanning direction and recording dots with an identical dot forming element, while carrying out the sub-scan by the combination of feeding amounts in respective intervals of adjoining shifts, so as to record a sub-scan-induced displacement detection pattern in each dot record mode. The sub-scan-induced displacement detection pattern is read with a sensor. Then the second displacement data is generated based on an output of the sensor.
This application enables the feeding errors of sub-scan to be evaluated based on the actual printing result. Since the identical dot forming element is used to record dots, the net feeding errors of sub-scan can be evaluated adequately.
The first displacement data may be generated according to the following procedure. Each of the dot forming elements are driven while shifting the dot record head in a direction identical with the main scanning direction, so as to print a head-induced displacement detection pattern. The head-induced displacement detection pattern is read with a sensor. Then the first displacement data is generated based on an output of the sensor.
This application enables the deviations of the dot recording positions in the sub-scanning direction with regard to the respective dot forming elements to be evaluated based on the actual printing result. Since dots are recorded without any sub-scan, the net deviations of the dot recording positions intrinsic to the respective dot forming elements can be evaluated adequately.
The technique of the present invention may be actualized by any of various applications listed below:
(1) a printing apparatus and a printing control apparatus;
(2) a printing method, a printing control method, and a method of manufacturing the printing apparatus;
(3) a dot record head;
(4) a method of manufacturing the dot record head;
(5) a computer program for actualizing any of the above apparatuses and methods;
(6) a recording medium in which the computer program for actualizing any of the above apparatuses and methods is recorded; and
(7) a data signal that includes the computer program for actualizing any of the above apparatuses and methods and is embodied in a carrier wave.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.